What Could Be Causing My Constipation and Overflow Diarrhea?

I’m 18 I’ve been having some bowel issues. Around 2 years ago, I had a big IBS flare up (according to my doctor) that lasted for a while. Just recently, after not having much problems since, I’ve been feeling constipated. This occurred after being under some stress from a couple school tests (though, to me, the stress didn’t seem that much different from other stresses I’ve had). I would feel the urge to poop, but very little would come out (even though I felt like there’s a big piece that needed to). When I would push any harder, I could maybe get some more small pieces to come out, though it would burn and be discomforting. This would go on for a while until recently I would have some mild diarrhea. I know this is a bad habit, but I did some reading on the internet and learned that I may be having overflow diarrhea. I still have the feeling of being backed up (that a big piece of poop needs to come out) and nauseous - however not much abdominal pain (yet). I just tried a suppository and unfortunately it led to nothing but some mucus coming out. I’ve been anxious about this, however I’ve started to wonder: Am I getting bowel issues because I’m nervous, or am I nervous because I’m getting bowel issues. I’m here because I’m wondering if all this is an IBS episode, or if this is something more urgent. Both my parents believe it’s nothing but IBS, however, I am a little concerned that it could be something more dire. I’ve been trying to keep my mind off of it, however it is quite hard after knowing a suppository wouldn’t work.